Diversity receiving system



Aug. 26, 1941. H. o. PETERSON DIVERSITY RECEIVING SYSTEM Filed Aug. 25, 1940 ATTORNEY Patented Aug. 26, 1941 DIVERSITY RECEIVING SYSTEM Harold O. Peterson, Riverhead,.N. Y., assigner to Radio Corporation of America, acorporation of'j Delaware Application August 23, 1940, serial No. v353,907

1i claims.

This invention relates to a jdiversty receiving systemfor the receptionof frequency or phase modulated signals.

--Itfis known in radio reception that signals are subject-tofading, the degree of which varies unpredictably; ;'In the transmission of amplitude modulatedrsignals, it has been proposed to climi-- nate. or reduce the variations inintensity of the received vsignal by providing at thereceiving station a plurality'of geographically spaced antennae in thesame or different planes of polarizationandftozieedthe energies collected by these antennae to a;- single signal responsive circuit. The-possibi1ity-ofgthe signal fading out equally at all of the'fspaced receiving yantennae at the same time gis, therefore,V reduced with increase in the `*nur nloer of "receiving antennae. Such known systems for overcoming fading are generally known as diversity receiving systems;

Y The present invention provides an improved diyersity'receiving system applicable particularly for t1'1 e' reception of frequencymodulated or phase modulated signals. 1 j n;

The -present invention also provides an improved and completely electrical systemfor selecting f or use thatfreceiver -of the "diversity system giving .the best results. AIn accordance with the inventionthe use of mechanically operating relaysvis completely avoided, and there'is provided a-systemcapable at all times of automatically sei lectingI the best of the available received signals. This selection Ais-olone continuouslywithout delay,

while at the same -time those receivers which have received feeble or `unsatisfactory signals'are eifectively-disassociated from* the utilization cir- A bettenunderstanding of the inventionnmay be'had-jby referring to the following description when rea-d in connection with the accompanying drawing, Twlfierein:1'v y i v :Fig. lfisfaschematic view of a diversity receiving system arranged in accordance with the principles ofithe invention;,and I 1 ..-Fig.f 2 is a fragmentary circuit diagram of on'e of the circuit elements of the system. In -Fig. 1,- the 'incoming frequency or phase modulated-signals are collected by antennas I; 2 anda which'ar-e locatedat geographically spaced points where thesignal does not fade similarly- Observations have shown that the receiving antennas needf'onlybe'separated from one another byadiStance of a fev;r hundreds of feetand less, in order to get this effect. These antennas may bepolarized in the sameplane or in :different planes! and; if desired, `:be of 'the 1 steerable direc-1 tive type in order to insure maximum reception. The'radio frequency v oltagesfrom eachantenna is selectively amplifiedfin a radio vfrequencyfamplier '4' and` then passed on rto a frequency C011- verter 5- in which the receivedv energy isheterodynedwith Venergyfrom alocal oscillator I0 to produce an intermediate frequency signal- -This intermediatefrequency signal is selectively amplified in ian intermediate frequency amplifier YI5 from which' the signalv 'energy is passedon to another frequency converter'f'I. In this-lastconverter the signal' energy combines With renergy from a local oscillator I.I to produce af lower intermediate frequency signal which is then passed on to intermediate' frequency amplifier 8. A Vportion ofthe output from amplifier 8 is passed on to a diode detector or suitable rectifier 9; The outputs' of all the.' diode detectors ,-9, Spass through resistors I5, rI 5 to acommon load resistor'lli from which the .direct current component of the drop is'utilized to controlhthe `gain of a preceding stage. The automatic gain control/voltage is passed through a time constant circuit composed of azresistor I'I and condenser I 8-, and over-.lead I4 to the control electrode of a preceding stage, or stages, here shown by Way of example Yas radio frequency amplier 4. f

The direct component of the voltage drop in resistor I6 appears as-a negative bias in the diode rectiflers 9,- 9-y in such a. manner that current flows in only that diode associated with the particular receiver having, at the moment, the largest incoming voltage in its associated antenna. As

an illustratiomif the antenna I happens; at any n one moment; to be receiving the strongest signal, we may assume,A as an example, that the alternat-l ing current voltage impressed-upon the particular diode detector rv9 associatedwithantenna I is of the order `of 5'0 Volts While thealternating current voltages impressed upon the other diode detectors associated with antennask 2 and 3 are Aless than 50yolts, let us say 15 and 10` volts, re-

stages. This particular rectifier 9 also serves in a manner described later, to control a valve unit to cause signal energy to pass therethrough.

The intermediate frequency energy from each amplifier 8 is passed on to an amplitude limiter I2 which provides a constant amplitude of alternating current output regardless of amplitude variations in the voltage fed into the limiter. Each limiter I2 is followed by a valve unit I3 which is so biased that it passes the intermediate frequency energy impressed upon it by the limiter only when current flows in the diodeV rectifier circuit 9 associated with its intermediate frequency amplifier 8. Putting it in other words, the action of the valve unit I3 is to feed signal energy into the next succeeding stage from only that antenna in which the signal is, at the moment, the strongest. valve units I3, I3, I3 is described in more detail hereinafter in connection with Fig. 2.

The outputs of the valve units I3, I3, I3 are fed into a common limiter I9 which also provides a constant amplitude of alternating current, from which the amplitude limited alternating current signal energy is fed into a detector 20 which may be either a phase modulation or a frequency modulation detector of a known type. This detector 20 produces an amplitude modu-A lated audio frequency signal which is a true reproduction of the original frequency or phase modulation, and which can be utilized in a suitable translator 2 I, the latter being a loudspeaker, a head set or a recorder. If desired, the output from the limiter I9 can be connected to a lower frequency suitable for transmission over a telephone line by means of a frequency converter 22 and a local heterodyne oscillator 23.

Fig. 2 shows one form of circuit which the valve unit I3 may take. This valve unit is composed of a screengrid vacuum tube 20 to whose control grid is fed intermediate frequency energy from limiter |27, through transformer 21. Output energy for use by the subsequent limiter stage I9 is taken from transformer 2B. Blas for the control grid of tube 29 is provided by a suitable battery 3I whose positive terminal is connected to the cathode of the tube and whose negative terminal is connected to the control grid over a path including resistor I5 (in the preceding diode circuit) and resistor 25. This Y bias is such that very little signal passes through the tube 29 when there is no direct current flowing through the resistor I5. The passage of direct current in resistor I5 produced by rectifier 9 will change the bias on the grid of tube 29 so as to make the bias less negative, by reason of which tube 29 will pass the intermediate frequency energy from the input circuit 21 tothe output circuit 28. It will thus beapparent that only that valve unit which is associated with the particular receiver having, at the moment, the largest incoming voltage in its antenna will function to supply intermediate frequency signal energy to the common limiter I9, and that the current flow condition of this valve unit is controlled by the output of its associated diode detector 9.

The apparatus described above is similar for each of the three receivers in the diversity system associated with the antennas I, 2 or 3, for which reason corresponding units for all three receivers have been designated by the same referenceV numerals. Y

It should be understood that the invention is not limited to the precise circuit arrangements illustrated and described, but that various modi- The operation of these Y fications may be made without departing from the spirit and scope of the invention.

What is claimed is:

l. A diversity receiving system comprising a plurality of spaced antennas, a receiver coupled to each antenna and including an amplifier, a valve unit coupled to the output of the amplifier of each receiver, a common receiving circuit coupled to the outputs of said valve units, a rectifier also coupled to the output of each amplifier for deriving a portion of the energy therefrom, an impedance in the space current path of each rectifier, and means for biasing each valve unit over a path including in series the said impedance of the rectifier associated with the same receiver, whereby the flow of current through a rectifier causes a direct current to flow through its associated impedance and produces a change in the bias of the valve unit in circuit therewith.

2. A diversity receiving system comprising a plurality of spaced antennas, a receiver coupled to each antenna and including an amplifier, a valve unit coupled to the output of the amplifier of each receiver, a common receiving circuit coupled to the outputs of said valve units, a rectifier also coupled to the output of each amplifier for deriving a portion of the energy therefrom, an impedance in the space current path of each rectifier, and means for biasing each valve unit over a path including inl series the said impedance of the rectifier associated with the same receiver, whereby the fioW of current through a rectifier causes a direct current to fiow through its associated impedance and produces a change in the bias of the valve unitin circuit therewith, a common load resistor coupled to said impedances, and an automatic gain control circuit eX- tending from said common load resistor to all of said individual receivers.

3. A diversity receiving system comprising a plurality of spaced antennas, a receiver coupled to each antenna and including an amplifier, a valve unit coupled to the output of the amplifier of each receiver, a common receiving circuit coupled to the outputs of vsaid valve units, a rectifier also coupled to the output of each amplifier for deriving a portion of the energy therefrom, an impedance in the space current path of Veach rectifier, and means for biasing each valve unit over a path including in series the said impedance of thel rectifier associated with the same receiver, whereby the fiow of current through a rectifier causes a direct current to flow through its associated impedance and'produces a change in the bias of the valve unit in circuit therewith, a common load resistor coupled to said impedances, and an automatic gain control circuit having a predetermined time-constant extending VVquency converter, a common receiving circuit coupled to said intermediate frequency amplifiers, a valve unit located between each intermediate frequency amplifier andA said common receiving biasing each valve unit over a path includinginv series the resistor of the rectifier associated with the same intermediate frequency amplifier, whereby the flow of current throughV a rectifier causes a direct current to flow through itsassociated resistor and changes the bias on the valvev in circuit therewith. n

5. A diversity receiving system comprising a plurality of spaced antennae, an amplifier coupled to each antenna, a frequency converter inthe output of each amplifier forrproducing an intermediate frequency, an intermediate frequency amplifier in the output of each frequency converter, a common receiving circuit coupled to said intermediate frequency amplifiers, means for selectively connecting to said common receiving circuit the output of only that intermediate frequency amplifier receiving the strongest signal, said means including a rectifier coupled to each intermediate frequency amplifier for rectifying a portion of the intermediate frequency signal and also a valve unit located in the path between said each intermediate frequency amplifier and said common receiving circuit, said means also including a connection from the output of each rectifier to the input of the valve unit associated with the same intermediate frequency amplifier, whereby direct current flowing in said connection changes the bias on said valve unit in circuit therewith.

6. A diversity receiving system for receiving yfrequency or phase modulated signals comprising a plurality of receivers, each receiving the same signal and so related to each other that the received signals vary differently at the several receivers with variations in transmission conditions, each of said receivers having means for converting the received signal to an intermediate frequency signal and an amplifier for amplifying said intermediate frequency signal, a rectifier coupled to each of said amplifiers, an electron discharge device circuit also coupled to each of said amplifiers and biased normally to pass very little current, a connection between each electron discharge device and the output of the rectifier associated with the same intermediate frequency amplifier, said connection serving to change the bias on said device when current flows through said rectifier, a limiter coupled in common to the outputs of said devices for providing a constant amplitude of alternating current output regardless of amplitude variations in the voltage fed into said limiter, and a detector circuit coupled to said limiter for changing the instantaneous variations in wavelengthA of the signal into an amplitude modulated signal.

7. A diversity receiving system for receiving frequency or phase modulated signals comprising a plurality of receivers, each receiving the same signal and so related to each other that the received signals vary differently at the several receivers with variations in transmission conditions, each of said receivers having means for converting the received signal to an intermediate frequency signal and an amplifier for amplifying said intermediate frequency signal, a rectifier coupled to each of said amplifiers, an electron discharge device circuit also coupled to each of said amplifiers and biased normally to pass very little current, a connection between each electron discharge device and a point in the space current path of the rectifier associated with the same intermediate frequency amplier, said connection serving to change the bias on said device whencurrent fiows through said rectifier, means coupled tosaid rectifiers for enabling only that rectifier to pass current which is associated with the receiver having, at the moment, the largest incoming voltage, a limiter coupled in common to the outputs of said devices for providing a constant amplitude of alternating current output regardless of amplitude variations in the voltage fed into said limiter, `and a detector circuit coupled to said limiter for changing the instantaneous variations in wavelength of the signal into anainplitude modulated signal.

8-.'A diversity receiving system for receiving frequency or phase modulated signals comprising a plurality of spaced antennae, a receiver coupled to each antenna and including an amplifier, a

common receiving circuit coupled to said receive ers,` a rectifier coupled to each amplifier1 an ramplitude limiter and a valve unit in the order named located between each amplifier and said common receiving circuit, a resistor in the space current path of each rectifier, -a volume control bias lead connected from the resistor of each rectifier to a preceding stage in each of said first receivers, and means for biasing each of said valve units over a path including in series the resistor of that rectier associated with the same receiver, whereby the fiow of current through a rectifier causes a direct current to flow through the resistor in its space current path and produces a change in the bias of the valve unit in circuit therewith, said valve units being normally biased to pass very little signal current, and the change in said bias produced by a flow of current through its associated resistor being in such sense as to cause the valve unit to pass appreciable current.

9. A diversity receiving system comprising a plurality of spaced antennas, a receiver coupled to each antenna and including an amplifier, a common receiving circuit coupled to said receivers, said common receiving circuit including an amplitude limiter and a detector in the order named, a rectifier individually coupled to the amplifier of each receiver, a valve unit located between each amplier and said common receiving circuit, an impedance in the space current path of each rectifier, and means for biasing each valve unit over a path including, in series, the impedance of that rectifier associated with the same receiver, whereby the flow of current through a rectifier causes a direct current to fiow through the impedance in its space current path and produces a change in the bias of the valve unit in circuit therewith, a common load resistor coupled to said impedances, and an automatic gain control circuit extending from said common load resistor to all of said individual receivers, said valve units being normally biased to pass very little signal current, and the change in said bias produced by a flow of current through its associated resistor being in such sense as to cause the valve to pass appreciable current.

10. A diversity receiving system comprising a plurality of spaced antennae, a receiver coupled to each antenna and including an amplifier, a common receiving circuit coupled to said receivers, a rectifier individually coupled to the amplifier of each receiver for deriving therefrom only a portion of the signal energy, an impedance in the output of each rectifier, a common load for said rectifiers and arranged to be in series withl each of said impedances, whereby the flow of current through any one rectier causes a direct current to flow through the impedance in its output and through said common load, and an automatic gain control connection from a point on said common load circuit to said rst mentioned receivers.

11. In a diversity receiving system having a plurality of receivers feeding a common utilization circuit, means for passing to said utilization circuit the signal from only that receiver having the largest incoming voltage, said means including a rectier associated with each receiver for rectifying only a portion of the alternating current in each receiver, and a common load resistor for said rectiers, whereby the passage of current through any one rectier produces a direct component of voltage drop in said load resistor which appears as a negative bias on said rectiers.

12. In a signaling system subject to variable transmission conditions, a plurality of receivers each receiving the same signal and so related to each other that the received signals vary indiierently at the several receivers with variations in transmission conditions, a common utilization circuit, separate paths extending from the outputs of said receivers to said common circuit, each of said paths including a space discharge device normally biased to be substantially nonconducting, and means associated with each receiver responsive solely to the largest incoming voltage for changing the bias of and rendering conductive the space discharge device in the output path ofthe same receiver.

13. A system in accordance with claim 1, characterized in this that said valve units constitute electron discharge devices.

14. A system in accordance with claim 5, characterized in this that each of said Valve units is normally biased to be substantially non-conducting in the absence of current through the rectifier in circuit therewith.

HAROLD O. PETERSON. 

